In radioimmunoassay procedures one of the critical features in determining the results is the complete separation of the soluble radiolabeled antigen from soluble complexes of antibody bound to radiolabeled antigen. In effecting this separation it is known to utilize zirconyl phosphate gel (Z-gel). The Z-gel binds proteins when the pH of the Z-gel is equivalent to or below the isoelectric point of the proteins. Thus, the Z-gel depends upon the charge of the protein. This characteristic limits the applicability of Z-gel since all immunological systems do not have a charge at which Z-gel is effective for the desired separation.
Charcoal and other adsorbents are also deficient in separating the antibody-antigen complex from unreacted antigen since they are not sufficiently specific and have shortcomings of stripping. Precipitation methods, including double antibody methods are disadvantageous since their use results in a loss of material during aspiration and decantation, balancing the proportion of proteins to prevent non-specific binding and interference of sample constituents preventing precipitation by a second antibody.
There is thus a need for a system which provides complete separation of the antigen-antibody complex from the unreacted antigen without undesirable processing and specificity problems.